I was ignoring the 92% percent part of it in my original comment when I said "not even open-source" because I think pretty much all privacy advocates know that it is built on top of Chromium.

I am not sure what your true source is, but mine is this from where I am quoting:

We don’t publish it under an open-source license and only release obfuscated versions of it. The obfuscation is partly there to improve performance, but it also very much is the first line of defense, to prevent other parties from taking the code and building an equivalent browser (essentially a fork) too easily.

While they release the source code of the UI elements, it seems that they only release a obfuscated version of the UI source code, which I am afraid won't go well If I want to easily "audit and go through". Though it's possible they have now changed their minds and my news sources are outdated.